Methods of making fiber optic connector sub-assemblies

ABSTRACT

A method of making a fiber optic connector sub-assembly involves: initially disposing a bonding agent in a ferrule bore of a ferrule; heating at least a portion of the ferrule above a melting temperature of the bonding agent so that some of the bonding agent melts; and solidifying the bonding agent that has melted to form the fiber optic connector sub-assembly, all without an optical fiber being disposed within the ferrule bore.

PRIORITY APPLICATIONS

This application is a continuation of PCT Application No.PCT/US2016/045783, filed on Aug. 5, 2016, which is a continuation ofU.S. Pat. No. 9,581,768, filed on Oct. 19, 2015, which claims thebenefit of priority of U.S. Provisional Application Ser. No. 62/208,131filed on Aug. 21, 2015. The content of each of these applications isrelied upon and incorporated herein by reference in its entirety.

BACKGROUND

This disclosure relates generally to optical connectivity, and moreparticularly to fiber optic connector sub-assemblies having a ferruleand bonding agent disposed in the ferrule, along with methods of makingsuch sub-assemblies.

Optical fibers are useful in a wide variety of applications, includingthe telecommunications industry for voice, video, and datatransmissions. In a telecommunications system that uses optical fibers,there are typically many locations where fiber optic cables that carrythe optical fibers connect to equipment or other fiber optic cables. Toconveniently provide these connections, fiber optic connectors are oftenprovided on the ends of fiber optic cables. The process of terminatingindividual optical fibers from a fiber optic cable is referred to as“connectorization.” Connectorization can be done in a factory, resultingin a “pre-connectorized” or “pre-terminated” fiber optic cable, or thefield (e.g., using a “field-installable fiber optic connector).

Regardless of where installation occurs, a fiber optic connectortypically includes a ferrule with one or more bores that receive one ormore optical fibers. The ferrule supports and positions the opticalfiber(s), which are secured within a bore of the ferrule using a bondingagent. Some bonding agents have been specifically developed to allow“pre-loading” the bonding agent into the ferrule bore prior to aconnectorization process. Despite these developments, there remains roomfor improvement.

SUMMARY

One embodiment of this disclosure relates to a fiber optic connectorsub-assembly that includes a ferrule having a front end, a rear end, anda ferrule bore extending between the front and rear ends along alongitudinal axis. The fiber optic connector sub-assembly also includesa bonding agent disposed in the ferrule bore and having first and secondends along the longitudinal axis. The bonding agent has been melted andsolidified at the first and second ends. Furthermore, in someembodiments at least a portion of the bonding agent between the firstand second ends has not been melted and solidified.

Another embodiment of a fiber optic connector sub-assembly includes aferrule having a front end, a rear end, and a ferrule bore extendingbetween the front and rear ends along a longitudinal axis. The ferrulebore includes a first section extending inwardly from the rear end ofthe ferrule and having a first width, a second section extendinginwardly from the front end of the ferrule and having a second widththat is less than the first width, and a transition section locatedbetween the first section and the second section. The fiber opticconnector sub-assembly also includes a bonding agent disposed in atleast a portion of both the transition section and the second section ofthe ferrule bore. At least some of the bonding agent in the secondsection of the ferrule bore has been melted and solidified.

Methods of making a fiber optic connector sub-assembly are alsodisclosed, wherein the fiber optic connector sub-assembly includes aferrule having a front end, a rear end, a ferrule bore extending betweenthe front and rear ends along a longitudinal axis. One example of suchmethods comprises: (a) initially disposing a bonding agent in theferrule bore; (b) heating at least a portion of the ferrule above amelting temperature of the bonding agent initially disposed in theferrule bore so that some of the bonding agent melts; and (c)solidifying the bonding agent that has melted in step (b) to form thefiber optic connector sub-assembly. The bonding agent has first andsecond ends along the longitudinal axis that have been melted andsolidified following steps (b) and (c). Additionally, a portion of thebonding agent initially disposed in the ferrule bore in step (a) remainsbelow the melting temperature of the bonding agent during steps (b) and(c) so as to not melt and solidify during steps (b) and (c).

Another example of methods disclosed herein involves a ferrule having afront end, a rear end, a ferrule bore extending between the front andrear ends along a longitudinal axis, wherein the ferrule bore includes afirst section extending inwardly from the rear end of the ferrule andhaving a first width, a second section extending inwardly from the frontend of the ferrule and having a second width that is less than the firstwidth, and a transition section located between the first section andthe second section. According to this example, the method comprises: (a)initially disposing a bonding agent in at least the transition sectionof the ferrule bore; (b) heating at least a portion of the ferrule abovea melting temperature of the bonding agent initially disposed in theferrule bore so that at least some of the bonding agent melts; and (c)solidifying the bonding agent that has melted in step (b), wherein atleast some of the bonding agent that has been melted and solidified isdisposed in the second section of the ferrule bore.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the technical field of optical communications. It is to beunderstood that the foregoing general description, the followingdetailed description, and the accompanying drawings are merely exemplaryand intended to provide an overview or framework to understand thenature and character of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding, and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiment(s), andtogether with the description serve to explain principles and operationof the various embodiments. Persons skilled in the technical field ofoptical connectivity will appreciate how features and attributesassociated with embodiments shown in one of the drawings may be appliedto embodiments shown in others of the drawings.

FIG. 1 a perspective view of an example of a fiber optic connector;

FIG. 2 is an exploded side view the fiber optic connector of FIG. 1;

FIG. 3 is a cross-sectional view of a fiber optic connector according toanother embodiment;

FIG. 4 is a cross-sectional view of an example of a fiber opticconnector sub-assembly for the fiber optic connector of FIG. 2, whereinthe fiber optic connector sub-assembly includes a ferrule and bondingagent disposed in the ferrule;

FIGS. 5-11 are schematic views that sequentially illustrate an exampleof a method of forming a fiber optic connector sub-assembly according toan embodiment of this disclosure;

FIGS. 12-14 are schematic views illustrating an example of a heatingprocess for a method of forming a fiber optic connector sub-assemblyaccording to another embodiment of this disclosure.

FIG. 15 is a schematic view of one example of an arrangement forcarrying out methods according to some embodiments of this disclosure.

FIG. 16 is a schematic view of another example of an arrangement forcarrying out methods according to some embodiments of this disclosure.

FIG. 17 is a schematic view of yet another example of an arrangement forcarrying out methods according to some embodiments of this disclosure.

FIGS. 18-23 are schematic views that sequentially illustrate a furtherexample of a method of forming a fiber optic connector sub-assembly.

DETAILED DESCRIPTION

Various embodiments will be further clarified by examples in thedescription below. In general, the description relates to fiber opticconnector sub-assemblies and methods of making the same. Thesub-assemblies and methods may facilitate the cable assembly process fora fiber optic cable. That is, the sub-assemblies and methods may beinitial steps to facilitate terminating one or more optical fibers froma fiber optic cable with a fiber optic connector to form a cableassembly. One example of a fiber optic connector (also referred to as“optical connector 10”, or simply “connector 10”) for such a cableassembly is shown in FIG. 1. Although the connector 10 is shown in theform of a SC-type connector, the methods described below may beapplicable to processes involving different fiber optic connectordesigns. This includes ST, LC, FC, MU, and MPO-type connectors, forexample, and other single-fiber or multi-fiber connector designs. Ageneral overview of the connector 10 will be provided simply tofacilitate discussion.

As shown in FIGS. 1 and 2, the connector 10 includes a ferrule 12 havinga front end 14 (“mating end”) and rear end 16 (“insertion end”), aferrule holder 18 having opposed first and second end portions 20, 22,and a housing 24 (also referred to as “inner housing 24” or “connectorbody 24”). The rear end 14 of the ferrule 12 is received in the firstend portion 20 of the ferrule holder 18 while the front end 14 remainsoutside the ferrule holder 18. The second end portion 22 of the ferruleholder 18 is received in the housing 24. A spring 26 may be disposedaround the second end portion 22 and configured to interact with wallsof the housing 24 to bias the ferrule holder 18 (and ferrule 12).Additionally, a lead-in tube 28 may extend from a rear end of thehousing 24 to within the second end portion 22 of the ferrule holder 18to help guide the insertion of an optical fiber (not shown in FIGS. 1and 2) into the ferrule 12. An outer shroud 32 (also referred to as“outer housing 32”) is positioned over the assembled ferrule 12, ferruleholder 18, and housing 24, with the overall configuration being suchthat the front end 16 of the ferrule 12 presents an end face configuredto contact a mating component (e.g., another fiber optic connector; notshown).

In a manner not shown herein, a fiber optic cable providing the opticalfiber also includes one or more layers of material (e.g., strength layerof aramid yarn) that may be crimped onto a rear end portion 30 of thehousing 24, which is why the housing 24 may also be referred to as a“crimp body” or “retention body”. A crimp band (or “crimp ring”) may beprovided for this purpose. Additionally, a strain-relieving boot may beplaced over the crimped region and extend rearwardly to cover a portionof the fiber optic cable. Variations of these aspects will beappreciated by persons familiar with the design of fiber optic cableassemblies. For example, other ways of securing a fiber optic cable tothe housing 24 are also known and may be employed in some embodiments.Again, the embodiment shown in FIGS. 1 and 2 is merely an example of afiber optic connector to which the fiber optic connector sub-assembliesand methods provided in this disclosure may relate.

FIG. 3 illustrates the connector 10 in further detail, and FIG. 4 is anenlarged view of the ferrule 12 in isolation. The ferrule 12 may be thesame as that described in U.S. Pat. No. 8,702,322 (“the '322 patent”),which describes many details related to the geometry of the ferrule, thelocation of a bonding agent within a bore of the ferrule, and possiblecompositions for the bonding agent, this information being incorporatedherein by reference. In general, the ferrule 12 includes a ferrule bore102 extending between the front and rear ends 14, 16 along alongitudinal axis A1. More specifically, the ferrule bore 102 has afirst section 104 extending inwardly from the rear end 16 of the ferrule12, a second section 108 (also referred to as “micro-hole” or“micro-hole section”) extending inwardly from the front end 14 of theferrule 12, and a transition section 112 located between the firstsection 104 and the second section 108. The first, second, andtransition sections 104, 108, 112 have respective lengths L1, L2, and L3measured along or parallel to the longitudinal axis A1. The front andrear ends 14, 16 define respective front and rear end faces of theferrule 12 that extend in planes parallel or substantially parallel toeach other but substantially perpendicular to the longitudinal axis A1.In some embodiments, the front end face may be at a slight anglerelative to the longitudinal axis A1 to provide, for example, an angledphysical contact (APC) end face.

Still referring to FIGS. 3 and 4, the first section 104 of the ferrulebore 102 has a first width, and the second section 108 has a secondwidth less than the first width such that the transition section 112provides a decrease in width between the first section 104 and secondsection 108. More specifically, in the embodiment shown, the firstsection 104 of the ferrule bore 102 is a cylindrical bore extending fromthe rear end 16 of the ferrule 12 to the transition section 112 suchthat the first width is a first diameter D1. The second section 108 ofthe ferrule bore 102 is a cylindrical bore extending from the front end14 of the ferrule 12 to the transition section 112 such that the secondwidth is a second diameter D2. Accordingly, the transition section 112provides a decrease in diameter between the first section 104 and secondsection 108.

As shown in FIGS. 3 and 4, a bonding agent 120 is at least partiallylocated in the transition section 112 of the ferrule bore 102. Thebonding agent 120 may be pre-loaded or stored within the ferrule 100 fora significant amount of time (e.g., at least an hour, a day, a year,etc.) before inserting an optical fiber into the ferrule bore 102. Forexample, as mentioned above, the bonding agent 120 may be pre-loadedinto the ferrule bore 102 by the manufacturer of the ferrule 100. Thecombination of the ferrule 12 and bonding agent 120 pre-loaded thereinrepresents a fiber optic connector sub-assembly 130.

The '322 patent describes how the bonding agent 120 may be afree-flowing powder material coupled within the transition section 112of the ferrule bore 102 via compression. Several additional oralternative steps may be taken, as will be described in greater detailbelow, to produce the fiber optic connector sub-assembly in an evenfurther advantageous manner. First, however, exemplary bonding agentswill be summarized to further provide context for theseadditional/alternative steps.

Exemplary Bonding Agents

Although the discussion of possible bonding agents in the '322 patenthave been incorporated herein by reference, additional details relatingto such bonding agents can be found in U.S. Pat. No. 8,696,215 (“the'215 patent”) and U.S. Patent Application Pub. No. 2015/0098679 (“the'679 publication”), such details also being incorporated herein byreference. Some information from the '322 patent and/or the '215 patentand '679 publication is summarized below for quick reference.

The bonding agents in the '322 patent, the '215 patent, and '679publication are configured to be heated and cooled relatively quickly tofacilitate the termination process of a fiber optic cable, yet are alsoconfigured to provide sufficient coupling between the optical fiber(s)of a fiber optical cable and the ferrule bore. One specific example ofthe bonding agent is one that comprises a partially cross-linked polymerresin and a coupling agent that provides chemical coupling between thepolymer resin and optical fiber(s), the ferrule 12, or both. Thepresence of the coupling agent allows the polymer resin to be selectedprimarily for heating and cooling properties rather than adhesionproperties. The bonding agent may even comprise a majority of thepolymer resin so as to be largely characterized by the heating andcooling properties of the polymer resin. For example, the bonding agentmay comprise between about 0.1 to about 10 parts by weight of thecoupling agent per 100 parts by weight of the partially cross-linkedpolymer resin.

As used herein, “cross-linked” or “cross-linking” refers to the chemicalbonding that connects a polymer chain to an adjacent polymer chain;“partially cross-linked” is where not all adjacent chains are bonded;and “partially cross-linkable” describes a chemical species that becomespartially cross-linked when sufficient heat is applied. It should beunderstood that the terms “partially cross-linked” and “partiallycross-linkable” describe the same polymer resin before or afterpartially cross-linking. For example, a polymer resin may be describedas partially cross-linkable when it is loaded into a ferrule and has notyet been heated to a temperature that results in the polymer resinpartially or completely cross-linking.

One example of a partially cross-linkable polymer resin with desirableheating and cooling characteristics is poly(phenylene sulfide). Oneexample of a coupling agent having desirable adhesion characteristics isa coupling agent having a silane functional group, such as one or moreof the following: an alkoxysilane, an oxime silane, an acetoxy silane, azirconate, a titanate, a silane with an epoxy ring on one end andtrimethoxy functional group at the other end, or combinations thereof.Other examples of partially cross-linkable polymers, coupling agents,and bonding agents are described in the '322 patent and '215 patents.

As mentioned above, the bonding agent may be a free-flowing powdermaterial prior to being heated above a cross-linking temperature for thepurpose of securing one or more optical fibers in a ferrule. The powdermay bay a result of grinding various components of the bonding agent(e.g., the partially cross-linkable resin) that are initially solid into respective powders, and then mixing powders thoroughly together. Somecomponents of the bonding agent (e.g., the coupling agent) may be aliquid, but the fraction such components in the blend may be relativelysmall (e.g., less than 10 parts by weight of the overall blend) so thatthe resulting blend is still considered a free-flowing powder. Forexample, in one embodiment, the coupling agent may be pre-reacted withthe thermoplastic powders in an organic solvent under refluxingconditions. After removal of the solvent, the treated powder remains.Under the conditions of refluxing solvent, some of the coupling agentmay have become permanently bonded to the polymer.

The partially cross-linkable polymer resin material of the bonding agenthas a melting temperature less than the cross-linking temperature. Forexample, the partially cross-linkable polymer resins above may each havea melting point at temperatures of less than 250° C., 270°, or 290° C.,yet each have a cross-linking temperature (i.e., the temperature atwhich the resin materials cross-link in the presence of air) of at least300° C., 325° C., or even 350° C.

Securing the Bonding Agent

Having described exemplary bonding agents, a method of making the fiberoptic connector sub-assembly 130 (FIG. 4) that includesadditional/alternative steps will now be described with reference toFIGS. 5-11. The bonding agent 120 may be initially disposed (i.e.,loaded) in the ferrule bore 102 using a loading device 140. In theembodiment shown, the loading device 140 includes a hollow tube 142(“outer rod”) and an inner rod 144 that is slidably received in the tube142. The loading device 140 is configured to collect a predeterminedamount of the bonding agent 120. Referring specifically to FIG. 5, theinner rod 144 has an outer diameter that is substantially the same as(i.e., equal to or within 5% of) an inner diameter of the tube 142, suchthat the inner rod 144 is closely received in the tube 142. The innerrod 144 is initially set in a retracted position relative to the tube142 so that a front end 146 of the inner rod 144 is recessed relative toa front end 148 of the tube 142. A cavity 150 defined by this recesscorresponds to the predetermined amount of the bonding agent 120 tocollect.

As shown in FIG. 6, the loading device 140 may then be pressed down intoa supply of the bonding agent 120 so that the cavity 150 is packed orotherwise filled with the bonding agent 120. The loading device 140 maythen be positioned next to the ferrule 12 (FIG. 7) with the cavity 150aligned with the ferrule bore 102. After contacting the rear end 16 ofthe ferrule 12 with the front end 148 of the tube 142 (FIG. 8), theinner rod 144 may be advanced/moved relative to the tube 142 and intothe ferrule bore 102 (FIG. 9) to move the bonding agent 120 into adesired location within the ferrule bore 102. As mentioned above,examples of desirable locations of the bonding agent 120 within theferrule bore 102 are discussed in the '322 patent and incorporatedherein by reference.

Before or after removing the loading device 140 from the ferrule 12, atleast a portion of the ferrule 12 may be heated above a meltingtemperature of the bonding agent 120. FIG. 10 schematically illustratesthe ferrule 12 being heated at first and second locations by first andsecond heating sources 160, 162. The first location may generallycorrespond to the beginning of the micro-hole section 108 of the ferrulebore and/or a first end 164 of the bonding agent 120 (i.e., the firstlocation may be a location on an outer surface 170 of the ferrule 12that is substantially the same distance from the front end 14 as thebeginning of the micro-hole section 108 and/or the first end 164 of thebonding agent 120). The second location may generally correspond to asecond end 166 of the bonding agent 120 (i.e., the second location maybe a location on the outer surface 170 of the ferrule 12 that issubstantially the same distance from the front end 14 as the second end166 of the bonding agent 120). Alternatively or additionally, the secondlocation may generally correspond to the end of the first section104/beginning of the transition section 112.

In other embodiments, the ferrule 12 may be heated at only a singlelocation or at more than two locations, and there may be only a singleheating source or more than two heating sources. The ferrule 12 mayalternatively or additionally be moved relative to one or more heatingsources, or vice-versa, to heat a portion of the length of the ferrule12 in a more continuous manner. Specific examples relating to theabove-mentioned possibilities will be described in more detail below.

Regardless of how the ferrule 12 is heated with the one or more heatingsources, some of the bonding agent 120 melts as a result of the heatingprocess. In particular, at least the first and second ends 164, 166 ofthe bonding agent 120 melt. The melted bonding agent is then allowed tocool (either passively or actively) to solidify. FIG. 11 illustrates howthe portion of the bonding agent 120 that has been melted and solidifiedmay form a solid crust 172 (“crust portion”) around a portion 174 of thebonding agent that has not been melted and solidified. The crust portion172 of the bonding agent 120 is no longer in a powder form. There issome crystallinity in the crust portion (e.g., the crust portion mayhave a spherulipic crystallinity of about 20-60%).

The other portion 174 of the bonding agent 120, on the other hand,remains in a powder form in this embodiment (and, therefore, may bereferred to as the “powder portion” or “powder material” of the bondingagent). For example, the powder portion 174 may still comprise particlesof the bonding agent 120 material having an average size (e.g., maximumdiameter or width) between 8 and 100 microns. The powder portion 174 isnot crystalline (and not quenched), and instead is amorphous.

There are various ways to characterize the difference between the crustportion 172 and powder portion 174 other than the distinction between asolid region and powder region. For example, the crust portion 172 mayhave a density between about 1.0 grams per cubic centimeter (g/cc) and1.5 g/cc (and specifically between about 1.3 g/cc and 1.4 g/cc in someembodiments), whereas the powder portion 174 may have a bulk or untappeddensity that is less, such as between about 0.4 and 0.6 g/cc. Stateddifferently, the crust portion 172 may have a density that is at least1.5, 2, or even 3 times the bulk/untapped density of the powder portion174.

There are also various ways to characterize the extent of the crustportion 172. For example, the bonding agent 120 has an axial length I₀measured along the longitudinal axis A1 between the first and secondends 164, 166. The first and second ends 164, 166 may be part ofrespective first and second regions of the bonding agent 120 that eachrepresent between about 1% and about 33% of the overall axial length I₀of the bonding agent 120. Stated differently, and as shown in FIG. 11,the first and second regions may have respective axial lengths I₁ and I₂that are between about 1% and about 33% of the overall axial length I₀.The first and second regions may alternatively be characterized withreference to the diameter D1 (FIG. 4) of the first section 104 of theferrule bore 102. For example, the first and second regions haverespective axial lengths I₁ and I₂ that are each between about 1% andabout 50% of the outer diameter D1. In some embodiments (including anyof those mentioned above), at least 90% of the bonding agent 120 in thefirst region has been melted and solidified (i.e., is in the form ofcrust portion 172). In these or other embodiments, at least 90% of thebonding agent 120 in the second region has been melted and solidified(i.e., is in the form of crust portion 172).

As shown in FIG. 11, the crust portion 172 may even be formed in aperipheral region of the bonding agent 120 that is between the first andsecond ends 164, 166 and in contact with the surface of the ferrule bore102. The powder portion 174 then comprises a central region of thebonding agent 120 surrounded by the peripheral region. In someembodiments, the crust portion 172 may have a thickness T between about1% and about 30% of the outer diameter D1 (FIG. 4; the thickness T ismeasured from where the bonding agent 120 contacts the surface of theferrule bore 102 to the nearest location of the crust portion 172).Although FIG. 11 illustrates the crust portion 172 being formed aroundan entire periphery of the bonding agent 120, in some embodiments onlythe first and second ends 164, 166 of the bonding agent 120 may form acrust portion.

As can be appreciated, by forming the crust portion 172 in at least thefirst and second ends 164, 166 of the bonding agent 120, the bondingagent 120 is more securely coupled to the ferrule bore 102 compared tothe situation where no amount of the bonding agent 120 has been meltedand solidified. This helps preserve the predetermined amount of thebonding agent 120 in the ferrule bore 102 between the time of formingthe fiber optic connector sub-assembly 130 and the time when the fiberoptic connector sub-assembly 130 is used during a cableassembly/termination process. The period between times may besignificant, such at least a day, a week, a month, or even a year. Andduring this period, the fiber optic connector sub-assembly 130 may betransported and otherwise handled in various manners. The likelihood ofthe bonding agent 120 migrating out of the ferrule 12 during this periodmay be reduced or eliminated by forming the fiber optic connectorsub-assembly 130 in the manner described above.

In addition to helping preserve the predetermined amount of the bondingagent 120 in the ferrule bore 102, forming the crust portion 172 alsohelps preserve the bonding agent 120 in the location where the bondingagent 120 is initially disposed in the ferrule bore 102. The improvementin consistency simplifies or otherwise facilitates termination processesinvolving the fiber optic connector sub-assembly 130.

Furthermore, when the bonding agent 120 comprises a partiallycross-linkable polymer resin, the heating of the bonding agent 120 maybe carefully controlled so that the crust portion 172 melts andsolidifies without irreversible chemical bonding between adjacentpolymer chains of the polymer resin. This may be achieved by heating theferrule 12 (and, ultimately, portions of the bonding agent 120) abovethe melting temperature of the bonding agent, but below thecross-linking temperature of the bonding agent. One of the advantages ofsuch a process is that the resulting fiber optic connector sub-assembly130 not only has the bonding agent 120 more securely coupled to theferrule bore 102, but also preserves the ability of the bonding agent120 to form even greater adhesion properties at a later point in time.In particular, the irreversible cross-linking and greatest adhesionproperties of the bonding agent 120 can be reserved for the cableassembly/termination process in which the fiber optic connectorsub-assembly 130 is eventually used.

Now that methods of forming the fiber optic connector sub-assembly 130have been introduced, some more specific examples relating to theheating process will be described. The first and second heating sources160, 162 in FIG. 10 are shown in a generic manner because any suitableheating source may be used to heat the ferrule 12. For example, theheating source(s) associated with the heating process may comprise oneor more laser(s), oven(s), resistive wire(s) wrapped around the ferrule,or the like.

In the embodiment shown in FIGS. 12-14, a single heating sourcerepresents a laser 180 that is first used to irradiate the ferrule 12 atthe first location. If desired, the ferrule 12 may be rotated relativeto the laser 180, or vice-versa, to irradiate all or portions of thecircumference of the ferrule 12 at the first location. Relative axialmovement may then be initiated between the ferrule 12 and laser 180(i.e., the ferrule 12 may be moved relative to the laser 180, orvice-versa, in a direction along or parallel to the longitudinal axisA1) to bring a beam of the laser 180 into alignment with the secondlocation. At this point, and as schematically shown in FIG. 13, thelaser 180 may then be operated to irradiate the ferrule 12 at the secondlocation. Again, if desired, the ferrule 12 may be rotated relative tothe laser 180, or vice-versa, to irradiate all or portions of thecircumference of the ferrule 12.

One of the advantages of irradiating the ferrule 12 at two or more axiallocations is that the bonding agent 120 can be more strategicallymelted. For example, attempting form a laser beam that spans a lengthbetween the two locations may not lead to uniform (or at least asuniform) melting of the bonding agent 120 where the melting is neededmost—namely, the first and second ends 164, 166 of the bonding agent—toprovide the above-mentioned benefits. This, in turn, may result in airvoids or other undesirable attributes in the crust portion 172.Nevertheless, the present disclosure does not exclude forming a laserbeam that spans a length of the ferrule 12 corresponding to a greaterportion or all of the axial length I₀ (FIG. 11) of the bonding agent120.

FIGS. 15-17 schematically illustrate various ways one or more lasers 180may be arranged relative to the ferrule 12. In FIG. 15, a reflector 182is used to direct a laser beam 184 at the ferrule 12, which may allowthe laser 180 to be positioned in an optimized manner. In FIG. 16, firstand second lasers 180 a, 180 b are used to emit respective first andsecond beams 184 a, 184 b that impinge opposite sides of the ferrule 12.Such an arrangement may be an effective way to heat the ferrule 12 andmelt some of the bonding agent 120 without relative rotation between theferrule 12 and one or more lasers, although such relative rotation maystill be initiated if desired. FIG. 17 illustrates an arrangementsimilar to FIG. 16, except that only a single laser 180 is used toirradiate opposite sides of the ferrule 12. The laser 180 emits a laserbeam 190 that is split into two beam portions 190 a, 190 b (or “legs”)by a beam splitter 192, with each beam portion 190 a, 190 b beingdirected by one or more reflectors 182 to impinge opposite sides of theferrule 12. Optical elements, such as lenses, may be positioned anywherein the path of the beam portions 190 a, 190 b to shape or otherwisefocus the beam portions 190 a, 190 b in a particular way, if desired.

Each of the arrangements in FIGS. 15-17, or variants thereof, may beused to heat the ferrule 12 at both the first and second locations,analogous to the single laser 180 in the embodiment discussed withreference to FIGS. 12-14. Alternatively, there may be a separate anddistinct setup or arrangement of one or more lasers for heating theferrule 12 at the first and second locations. For example, the ferrule12 may be positioned relative to a first arrangement of one or morelasers, heated at a first location, moved and positioned relative to asecond arrangement of one or more lasers, and then heated at a secondlocation. The first and second arrangements may be the same or differentarrangements.

Filling the Micro-Hole of the Ferrule Bore

In some instances, it may be desirable to fill the second section 108 ofthe ferrule bore 102 with the bonding agent 120 when forming the fiberoptic connector sub-assembly 130. For example, in some embodiments thefront end 14 of the ferrule 12 may be grinded or otherwise re-shapedprior to being installed on an optical fiber to form an end face with aspecific geometry (e.g., an angled physical contact (APC) end face).Such additional processing has the potential to deposit debris in thesecond section 108, which can make inserting an optical fiber during alater termination process challenging (and even impossible in someinstances). Even if there is no additional processing, the ferrule 12may be exposed during normal handling and transport to debris that alsohas the potential to migrate into and block the second section 108.Filling the second section 108 of the ferrule bore 102 may also helpensure that an optical fiber terminated with the ferrule 12 issurrounded by the bonding agent 120 within the second section 108 afterthe termination process. This, in turn, can improve adhesion strengthand reliability.

One of the challenges in filling the second section 108 of the ferrulebore 102 with the bonding agent 120 relates to the relatively small sizeof the ferrule bore 120. Simply loading the bonding agent 120 into theferrule bore 102 in the manner described above may not result in asufficient amount of the bonding agent 120 occupying the second section108. This may especially be the case when the bonding agent 120 isinitially disposed in the ferrule bore 102 in a powder form, as thesolid nature and size of particles in such a material may make itdifficult to locate the bonding agent 120 in the second section 108 ofthe ferrule bore 102. Moreover, even if there can be a substantialamount of the bonding agent 120 initially disposed in the second section108 in alternative embodiments, it is still desirable to melt andsolidify at least some of the bonding agent 120 for the reasonsmentioned above.

One example of a method for making the fiber optic connectorsub-assembly 130 with more bonding agent disposed in the second section108 of the ferrule bore 102 is shown in FIGS. 18-23. The bonding agent120 may be initially disposed in the ferrule bore 102 in the mannerdescribed above with reference to FIGS. 5-9 (e.g., using the loadingdevice 140) or in any other manner. The bonding agent 120 is initiallydisposed in the transition section 112 of the ferrule bore 102, althoughthere may be some amounts also disposed in the first and second sections104, 108 in some embodiments, as shown in FIG. 18. The amount of thebonding agent 120 initially disposed in the second section 108 in suchembodiments may be relatively small. For example, the bonding agent 120initially disposed in the ferrule bore 102 may occupy less than 50%,less than 25%, or even less than 10% of the volume of the second section108 in some embodiments.

To assist moving more of the bonding agent 120 into the second section108 of the ferrule bore 102 before or during a heating of the ferrule12, a nozzle 200 may be coupled to the rear end 16 of the ferrule 12.FIG. 19 schematically illustrates the nozzle 200 including an outlet 202communicating with the ferrule bore 102 at this point. Pressurized airor other gas may be supplied through the nozzle 200 and into the ferrulebore 102 to apply pressure to the bonding agent 120. The pressure canhelp force at least some of the bonding agent 120 from the transitionsection 112 into the second section 108, especially after heating andmelting at least some of the bonding agent 120.

To this end, FIGS. 20-22 schematically illustrate the ferrule 12 beingheated at first and second locations by a heating source 160. Theheating may be achieved using any of the principles discussed above. Forexample, there may alternatively be first and second heating sourceslike the embodiment in FIG. 10. The various methods of heating,including the different types, arrangements, and operation of heatingsources discussed with reference to FIGS. 10 and 12-17, remainpossibilities. The heating source 160 may represent one or more lasers,for example. In such embodiments, the laser beam(s) may even be focusedusing lenses or other optical elements to impinge over a longer lengthof the ferrule 12. This may be particularly advantageous for the heatingsource 160, as heating both a portion of the transition section 112 anda portion of the second section 108 when heating the ferrule 12 at thefirst location may help promote flow of the bonding agent 120 that hasmelted into the second section 108.

As can be seen in FIGS. 20 and 21, at least some of the bonding agent120 melts after heating the ferrule at a first location with the heatsource 160, and the melted bonding agent 120 eventually solidifies(e.g., through passive or active cooling) in the second section 108 ofthe ferrule bore 102. In the embodiment shown, at least some of thebonding agent 120 initially disposed in the transition section 112 hasmelted and flowed into the second section 108. As a result, there is anincreased amount of the bonding agent 120 in the second section 108.Indeed, in some embodiments, the bonding agent 120 may occupy at least90% of the volume of the second section 108 following the heating andsolidification.

The flow of the bonding agent 120 may be assisted by the pressurize airsupplied by the nozzle 200, as noted above. The nozzle 200 acts as anair coupling, forming a seal with the ferrule bore 102. The supply (notshown) of air or other gas to the nozzle 200 may be turned on before theheating source 160 to apply pressure before heating, and turned offshortly prior to or when the heating source 160 is activated.Alternatively, the supply may be kept on for a period of time while theheating source 160 is in operation. Other methods of applying pressureto the bonding agent 120 before or during the heating step will beappreciated. Additionally, rather than supplying pressurized air with anozzle, in some embodiments a vacuum (not shown) may be coupled to thefront end 14 of the ferrule 12 over the opening of the ferrule bore 102.The vacuum may be operated to assist at least some of the bonding agent120 that has melted in the transition section 112 to flow into thesecond section 108 of the ferrule bore 102.

In some embodiments, the heating source 160 may be controlled based onthe flow of the bonding agent 120 into the second section 108 of theferrule bore 102. For example, equipment may be used to monitor whensome of the bonding agent 102 reaches or exits the end of the ferrulebore 102. The heating source 160 may then be deactivated in response tothe detection of the bonding agent 120. This may help ensure that theheating process has been carried out long enough for the bonding agent120 to substantially or completely occupy the second section 108 of theferrule bore 102.

As can be appreciated from FIGS. 21 and 22, eventually the ferrule 12 isheated at the second location, similar to the embodiment discussed abovewith respect FIG. 10, to melt an additional amount of the bonding agent120. Like the embodiment in FIG. 10, the additional amount of thebonding agent 120 heated at this stage was initially disposed in theferrule bore 102. In alternative embodiments not shown, there may onlybe a small amount of the bonding agent 120 initially disposed in theferrule bore 102. After heating the first location of the ferrule 12 tomelt some or all of this small amount, and after allowing the meltedbonding agent 120 to solidify in the second section 108 of the ferrulebore 102 (similar to FIGS. 20 and 21), an additional amount of thebonding agent 120 may be loaded into either or both the first section104 and the transition section 112 of the ferrule bore 108. The ferrule12 may then be heated at the second location to melt at least some ofthis additional amount. Either way, the additional amount of the bondingagent 120 that melts when heating the ferrule 12 at the second locationis eventually cooled and solidified in either or both the first section104 and the transition section 112 of the ferrule bore 102.

FIG. 23 illustrates the fiber optic connector sub-assembly 130 resultingfrom the process shown in and described with reference to FIGS. 18-22.As can be appreciated, the bonding agent that has been melted andsolidified can still form a crust portion 174 around a portion 174 ofthe bonding agent that has not been melted and solidified. In thisregard, the fiber optic connector sub-assembly remains similar to theone discussed above with reference to FIG. 11, except that an increasedamount of the bonding agent 120 occupies the second section 108 of theferrule bore 102. Again, the bonding agent 120 may substantially orentirely occupy the second section 108 as a result of the process shownin and described with reference to FIGS. 18-22. Most or all of thebonding agent 120 in the second section 108 may be part of the crustportion 172. For example, at least 90% of the bonding agent 120 disposedwithin the second section 108 of the ferrule bore 102 may have beenmelted and solidified.

The portion 174 that has not been melted and solidified may be a powderportion 174, as mentioned above, when the bonding agent 120 is initiallydisposed in the ferrule bore 102 in a powder form. Therefore, thevarious ways of characterizing the difference between the crust portion172 and powder portion 174 mentioned above (e.g., differences incrystallinity and/or density) remain applicable.

Persons skilled in optical connectivity will appreciate additionalvariations and modifications of the elements disclosed herein. Suchpersons will also appreciate variations and modifications of the methodsinvolving the elements disclosed herein. For example, althoughembodiments are described above where less than all of the bonding agentis heated and solidified when forming a fiber optic connectorsub-assembly, in alternative embodiments all or substantially all of thebonding agent may be heated and solidified. In such embodiments, theheating may still be controlled so that the bonding agent does notirreversibly cross-link and/or end up with a high degree ofcrystallinity (e.g., a spherulipic crystallinity above 60%). Forexample, when the bonding agent comprises a partially cross-linkablepolymer resin like the ones disclosed here, the bonding agent may beheated to above 250° C. but kept below 350° C., or even 300° C.

In addition to appreciating these and other variations, skilled personswill appreciate alternatives where some of the steps described above areperformed in different orders. To this end, where a method claim belowdoes not actually recite an order to be followed by its steps or it isnot otherwise specifically stated in the claims below or descriptionabove that the steps are to be limited to a specific order, it is no wayintended that any particular order be inferred.

What is claimed is:
 1. A method of making a fiber optic connectorsub-assembly that includes a ferrule having a front end, a rear end, aferrule bore extending between the front and rear ends along alongitudinal axis, the method comprising: (a) initially disposing thebonding agent in the ferrule bore of the ferrule; (b) heating at least aportion of the ferrule above a melting temperature of the bonding agentinitially disposed in the ferrule bore so that some of the bonding agentmelts; and (c) solidifying the bonding agent that has melted in step (b)to form the fiber optic connector sub-assembly; wherein: the bondingagent has first and second ends along the longitudinal axis that havebeen melted and solidified following steps (b) and (c); and a portion ofthe bonding agent initially disposed in the ferrule bore in step (a)remains below the melting temperature of the bonding agent during steps(b) and (c) so as to not melt and solidify during steps (b) and (c). 2.The method of claim 1, wherein the bonding agent initially disposed inthe ferrule bore comprises a powdered material.
 3. The method of claim2, wherein the powdered material comprises particles of the bondingagent, the particles having an average size between about 5% and about10% of a minimum diameter of the ferrule bore.
 4. The method of claim 2,wherein the bonding agent that has been melted and solidified has adensity between about 1.0 g/cc and about 1.5 g/cc, and further whereinthe portion of the bonding agent between the first and second ends thathas not been melted and solidified during steps (b) and (c) has a bulkdensity that is less than 1.0 g/cc.
 5. The method of claim 2, whereinthe bonding agent that has been melted and solidified has a densitybetween about 1.3 g/cc and about 1.4 g/cc, and further wherein theportion of the bonding agent between the first and second ends that hasnot been melted and solidified during steps (b) and (c) has a bulkdensity that between about 0.4 g/cc and about 0.6 g/cc.
 6. The method ofclaim 2, wherein the bonding agent that has been melted and solidifiedhas a density that is at least 1.5 times the bulk density of the bondingagent between the first and second ends that has not been melted andsolidified during steps (b) and (c).
 7. The method of claim 2, whereininitially disposing the bonding agent in the ferrule bore in step (a)comprises packing the bonding agent into the ferrule bore viacompression.
 8. The method of claim 7, wherein the bonding agent ispacked into the ferrule bore by: loading a tube with the bonding agent,wherein the tube is hollow and an inner rod is slidably received in thetube, the inner rod being in a retracted position where a front end ofthe inner rod is recessed within the tube when loading the tube with thebonding agent; contacting the rear end of the ferrule with a front endof the tube when the tube has the bonding agent loaded therein; andsliding the inner rod relative to the tube and into the ferrule bore tomove the bonding agent out of the tube and into the ferrule bore.
 9. Themethod of claim 1, wherein heating at least a portion of the ferrule instep (b) comprises irradiating at least a portion of the ferrule with atleast one laser.
 10. The method of claim 9, wherein the ferrule isirradiated at two or more locations spaced apart between the front andrear ends of the ferrule.
 11. The method of claim 1, wherein: thebonding agent comprises a partially cross-linkable polymer resin; thepartially cross-linkable polymer resin has a melting point between about250° C. and about 350° C.; and the bonding agent that is melted in step(b) is kept below 350° C.
 12. The method of claim 1, wherein step (c) isperformed without any optical fiber being located in the ferrule bore.13. A method of making a fiber optic connector sub-assembly thatincludes a ferrule having a front end, a rear end, and a ferrule boreextending between the front and rear ends along a longitudinal axis,wherein the ferrule bore includes a first section extending inwardlyfrom the rear end of the ferrule and having a first width, a secondsection extending inwardly from the front end of the ferrule and havinga second width that is less than the first width, and a transitionsection located between the first section and the second section, themethod comprising: (a) initially disposing the bonding agent in at leastthe transition section of the ferrule bore without there being anyoptical fiber present in the ferrule bore; (b) heating at least aportion of the ferrule above a melting temperature of the bonding agentinitially disposed in the ferrule bore so that some of the bonding agentmelts; and (c) solidifying the bonding agent that has melted in step (b)to form the fiber optic connector sub-assembly without there being anyoptical fiber present in the ferrule bore; wherein: the bonding agenthas first and second ends along the longitudinal axis that have beenmelted and solidified following steps (b) and (c); and a portion of thebonding agent initially disposed in the ferrule bore in step (a) remainsbelow the melting temperature of the bonding agent during steps (b) and(c) so as to not melt and solidify during steps (b) and (c).
 14. Themethod of claim 13, wherein the bonding agent initially disposed in theferrule bore comprises a powdered material.
 15. The method of claim 14,wherein the bonding agent that has been melted and solidified has adensity between about 1.0 g/cc and about 1.5 g/cc, and further whereinthe portion of the bonding agent between the first and second ends thathas not been melted and solidified during steps (b) and (c) has a bulkdensity that is less than 1.0 g/cc.
 16. The method of claim 14, whereinthe bonding agent that has been melted and solidified has a density thatis at least 1.5 times the bulk density of the bonding agent between thefirst and second ends that has not been melted and solidified duringsteps (b) and (c).
 17. The method of claim 14, wherein initiallydisposing the bonding agent in the ferrule bore in step (a) comprisespacking the bonding agent into the ferrule bore via compression.
 18. Amethod of making a fiber optic connector sub-assembly that includes aferrule having a front end, a rear end, a ferrule bore extending betweenthe front and rear ends along a longitudinal axis, the methodcomprising: disposing the bonding agent in the ferrule bore of theferrule as a powdered material; heating at least a portion of theferrule above a melting temperature of the bonding agent initiallydisposed in the ferrule bore so that some of the powdered materialmelts; and solidifying melted bonding agent to form the fiber opticconnector sub-assembly; wherein a portion of the powdered materialinitially disposed in the ferrule bore remains below the meltingtemperature of the bonding agent when heating the at least a portion ofthe ferrule.
 19. The method of claim 18, wherein an optical fiber is notpresent in the ferrule bore during the disposing, heating, andsolidifying steps.
 20. The method of claim 18, wherein initiallydisposing the bonding agent in the ferrule bore comprises packing thebonding agent into the ferrule bore via compression.